The invention relates to coloured plastic granules obtained by mixing plastic granulate particles with colouring agent particles.
In the present application, a colouring agent is in general understood to mean a pigment; for particular applications, however, the term may relate to a soluble colouring agent.
Coloured plastic granules and also methods for the preparation of such granules are known from the Dutch Pat. application No. 6,508,802 in which a method is described for mixing a plastic, such as for example poly-vinyl chloride, with a 1 colour pigment at temperatures up to 150.degree. C. and subjecting said mixture to frictional forces and/or shear stresses, as a result of which the pigment particles are rubbed into the capillaries of the plastic particles.
This known method has the disadvantage that it is possible to process only pigments which are of particle size less than the capillaries of the plastic particles or that there has to be an appreciable hardness difference between the colouring agent particles and the plastic particles, the plastic particles having to have pores of which at least the edges are harder than the pigments which have to be absorbed by the plastic particles. A colouring agent which is much harder than the edges of the pores would in general only be capable of being processed if the size of the colouring agent particles is significantly less than the diameter of the pores. This implies that there is a significant limitation in the choice of colouring agents and plastics and that only certain combinations can be successfully processed.